1. Field of the Invention
The present invention relates to apparatus for and a method of generating voice messages. It has particular utility in relation to voice message generators which generate one or more types of message, each type of message having an invariable portion which is common to all such messages and a variable portion which normally differs from one such message to the next.
2. Related Art
In many examples of such voice message apparatus it is undesirable to record, in their entirety, all possible messages that might be output by the apparatus. Instead, benefits are gained by storing only one instance of the invariable portion (sometimes known as a carrier phrase) and using that in the generation of all messages of that type. The variable portion of the message giving message-specific information can then be output with the carrier phrase to generate a specific message.
In some cases recorded speech corresponding to each possible message-specific information can be used. In other cases, it is better to synthesise speech corresponding to the message-specific information.
To give an example of the former case, an information apparatus for use in a metropolitan railway network might be operable to output a chosen message for each of around 200 stations in the network. A carrier phrase for one type of message might then be `This train is now approaching . . . ` Any one of the 200 station names (the message specific information) might be inserted into the gap in generating a specific message. Those skilled in the art will realise that the cost and complexity of the information apparatus will be significantly reduced if a single recording of the carrier phrase is used for all of the 200 possible messages.
To give an example of the latter case, a voice message generator forms an important component in an apparatus operable to enable the telephonic retrieval of information stored in a database. If, say, the database contains the names and telephone numbers of millions of people, it is impractical to store a recording of every one of those names and corresponding numbers. Hence, voice messages output by such apparatuses include variable portions synthesised from a text signal representing the name and/or the number concerned. Again, a single recording of a carrier phrase such as `The number you require is . . . ` can be used in generating any possible message of that type.
However, a drawback of conventional voice message generators is that the carrier phrase may have characteristic qualities which are different from those of the message specific part. These qualities might include highness of voice, liveliness of intonation, speed of delivery, loudness and the like. This is especially so in messages containing both recorded and synthetic speech, since, owing to the constraints of conventional speech synthesis technology, it is likely that the synthesised voice will have lower pitch and duller intonation than the recorded voice.
Another situation in which such a disturbing change of quality might present a problem arises where a recorded word is inserted to the synthesised output of the text-to-speech apparatus. It might be necessary to do this because the text-to-speech apparatus is itself unable to say the word well.
The conventional solution to the above problems is to place a short pause before and/or after the variable portion of the message.